In regards to physical security what constitutes a "Campus"? Is there a definition somewhere which describes what makes up a campus appose to standard set office buildings?
Campus is one of those nebulous terms like 'site' that has no standard definition. In general a campus is a group of buildings sharing a common parcel (or contiguous parcels) of land. The 15th floor of a 60 floor building may be the 'campus' of a company, whereas the Microsoft campus in Redmond, Washington has many buildings on it.
Exceptions occur when there are small offices near a major campus, those may be considered their own campus, or part of the main one. Again continuing with Microsoft, they have several large offices in downtown Bellevue, Washington. Is that a different campus, or the same? I don't know.